The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Referring now to FIG. 1, a hard disk drive (HDD) 10 includes a hard disk assembly (HDA) 50 and a HDA printed circuit board (PCB) 14. The HDA PCB 14 comprises a buffer module 18 that stores data associated with the control of the HDD 10. The buffer module 18 may employ SDRAM or other types of low latency memory. A processor 22 is arranged on the HDA PCB 14 and performs processing that is related to the operation of the HDD 10.
A hard disk controller (HDC) module 26 communicates with the buffer module 18, the processor 22, a spindle/VCM (voice coil motor) driver module 30, and an input/output interface module 24. The input/output interface module 24 may include a serial interface module, a parallel interface module, a serial Advance Technology Attachment (ATA) interface module, or a parallel ATA interface module.
Additionally, the HDC module 26 communicates with a read/write (R/W) channel module 34. During write operations, the R/W channel module 34 encodes data that is to be written by a R/W device 59. The R/W device 59 may also be referred to as the R/W head 59. The R/W channel module 34 processes data for reliability using coding schemes such as error correction coding (ECC) and run length limited coding (RLL). During read operations, the R/W channel module 34 converts an analog output of the R/W head 59 into a digital signal. The digital signal is then decoded to recover the data written on the HDD 10.
The HDA 50 includes one or more circular recording surfaces called platters 52 that are used to store data. The platters 52 include a magnetic coating for storing data in terms of magnetic fields. The platters 52 are stacked on top of one another in the form of a spindle. The spindle comprising the platters 52 is rotated by a spindle motor 54. Generally, the spindle motor 54 rotates the platters 52 at a fixed speed during read/write operations. The spindle/VCM driver module 30 controls the speed of the spindle motor 54.
One or more actuator arms 58 move relative to the platters 52 during read/write operations. The spindle/VCM driver module 30 also controls the positioning of the actuator arm 58 by using mechanisms such as a voice coil actuator or a stepper motor. For example, a voice coil motor (VCM) 57, which is controlled by the spindle/VCM driver module 30, may be used to control the positioning of the actuator arm 58.
The R/W head 59 is located near a distal end of the actuator arm 58. The R/W head 59 includes a write element such as an inductor (not shown) that generates a magnetic field. The R/W head 59 also includes a read element (such as a magneto-resistive (MR) element, also not shown) that senses magnetic field on the platters 52. The HDA 50 includes a preamp module 60, which amplifies analog read/write signals.
When reading data, the preamp module 60 amplifies low-level signals received from the read element and outputs the amplified signal to the R/W channel module 34. While writing data, a write current is generated that flows through the write element of the R/W head 59. The write current is switched to produce a magnetic field having a positive or negative polarity. The positive or negative polarity is stored on the hard drive platters 52 and is used to represent data.
Referring now to FIG. 2, data is typically written on the platters 52 in concentric circles called tracks 70. The tracks 70 are divided radially into multiple sectors 72. A circumferential length 74 of sectors 72 decreases as the diameter of the tracks 70 decreases towards the center of the platters 52.
Before performing a read/write operation on a sector 72 of a track 70, the R/W head 59 locks onto the track 70 by referring to positioning information called servo information. Servo information is generally prewritten on the platters 52 and provides the positioning information that is used by the R/W head 59 to read and write data at correct locations on the platters 52.
Modern HDDs increasingly use self-servo-write (SSW) methods instead of using external equipment to write servo information. Disk drives that utilize SSW methods write servo information using the same R/W heads that are used to read/write regular data. When writing servo information using SSW methods, the R/W heads initially write a preliminary servo pattern comprising servo wedges written in spirals. Subsequently, by servoing on the spirals and based on the timing and positioning information derived from the spirals, the R/W heads write a final servo pattern comprising servo wedges written in circles.
Referring now to FIGS. 3A-3B, a HDD 11 may use a SSW module 28 to write servo information. In FIG. 3A, the SSW module 28 may communicate with the processor 22, the HDC module 26, the spindle/VCM driver module 30, and the R/W channel module 34. The SSW module 28 may generate control signals to write servo information on platters 52. For example, the SSW module 28 may generate control commands that control movement of the actuator arm 58 during servo writing. The HDC module 26 and the spindle/VCM driver module 30 may implement the control commands during SSW. The SSW module 28 may generate a servo pattern that is written on the platters 52 using the read/write device 59. Additionally, the SSW module 28 may utilize the processor 22 to verify the servo pattern by performing read-after-write operations.
During SSW, the platters 52 may rotate in direction A, and the actuator arm 58 may move in direction B as shown in FIG. 3B. Motion delimiters called crashstops may be used to prevent the actuator arm 58 from moving beyond safe limits. For example, the VCM 57 may cause the actuator arm 58 to move between crashstop 55 and crashstop 53 while the R/W head 59 writes servo spirals 80 between tracks 70. The crashstop 55 may be referred to as an outer diameter (OD) crashstop 55. The crashstop 53 may be referred to as an inner diameter (ID) crashstop 53. Spirals 80 may be written from ID to OD or from OD to ID. When spirals 80 are written, the actuator arm 58 is accelerated from a stationary position to a predetermined velocity by applying current to the VCM 57.
Referring now to FIG. 4, spirals comprise servo wedges (hereinafter spiral wedges). For example, spiral 0 comprises spiral wedges s0, spiral 1 comprises spiral wedges s1, etc. Since spiral wedges are written diagonally (i.e., in spirals), the position of spirals has variable radial and circumferential components.
The final servo wedges (hereinafter final wedges) f0, f1, etc. may be written after or while writing the spirals by servoing on the spirals. Since the final wedges are written radially, (i.e., in circles instead of spirals), the radial component of the position of final wedges may vary but the circumferential component of the position of the final wedges may be fixed.
When the final wedges are written, the final wedge f0 may overwrite spiral s0, final wedge f1 may overwrite spiral s1, and so on. Additionally, as the radius increases, the final wedge f1 may overwrite spiral s0, the final wedge f2 may overwrite spiral s1, and so on.